This invention relates to a transparent glass pane having a reflectance reducing coating which is a laminate of a plurality of oxide films. In particular the glass pane is to be used as a vehicular window glass that is installed in an inclined position as in the case of a current automobile windshield, and the coating is for reducing reflectance of visible light obliquely incident on the coated side of the glass pane.
There are various proposals of antireflection coatings for preventing or reducing the reflection of visible light from vehicular window glasses or windshields.
As a coating for the antireflection purpose it is known to use a fluoride film and/or a laminate of a plurality of transparent oxide films which have different refractive indices. For example, JP 61-189501 A (1986) shows a three-layer coating made up of a first layer which is in contact with the glass surface and formed of Al.sub.2 O.sub.3 or CeF.sub.3 having a refractive index of 1.60-1.80, a second layer formed of a ZrO.sub.2 /TiO.sub.2 mixture having a refractive index of 1.95-2.15 and a third layer which is formed of MgF.sub.2 and has a refractive index of 1.30-1.45. JP 64-70701 A (1989) shows an antireflection three-layer coating which is electrically conductive and consists of a metal film coated on the glass surface as the first layer, a second layer which is a metal oxide film having a refractive index of 1.90-2.50 such as a TiO.sub.2 film and a third layer which has a refractive index of 1.35-1.50 and is formed of either SiO.sub.2 or MgF.sub.2. As a modified way of using a fluoride, JP 3-17601 A (1991) proposes to form an antireflection coating by applying a solution of a metal oxide precursor such as a silicon alkoxide to a glass surface, heating the sol film on the glass surface to convert it into a gel film and further heating the gel film in a fluorine containing atmosphere to thereby form a metal oxide film containing fluoride of the metal.
However, for vehicular window glasses, fluoride containing coatings are generally insufficient in durability, and the use of fluorine or a fluoride often offers inconvenience to the industrial manufacturing operations.
Besides, in the present invention an important matter of concern is the angle of incidence of visible light on a glass pane. In devising conventional anti-reflection coatings, attention is mostly paid to the reflection of perpendicularly or nearly perpendicularly incident light. However, in general the reflection reducing effect of a coating depends on the angle of incidence and greatly lowers when incident light makes an angle larger than about 50 degrees with the normal to the coated glass surface.
In the current automobiles, by way of example, it is prevailing to install the windshield in a steeply inclined position, and hence it is not rarely that the driver is irritated by the reflection of the dashboard in the windshield. Such a reflection phenomenon is unfavorable for the safety of driving.